The attack happened while the streetcar was in the Pearl District and a microchip in the pit bull was traced to a woman in Colorado.

According to Sgt. Pete Simpson, officers investigated the incident and spoke to witnesses but found no apparent criminal behavior. Neither dog owner was arrested or issued a citation, although the investigation is continuing.

Neither dog was registered with the county as a service animal, and Portland Streetcar policy is that only service animals are allowed.

But the Pomeranian’s owner told investigators her dog was a service animal and has papers from her physician that say that.

A new streetcar rolls through Portland, June 11, 2013. (KOIN 6 News)

“(Streetcar) drivers are basically allowed to ask two questions. Is this a service dog required because of a disability and what specific task is that dog doing to help a person with a disability?” said Dan Bower, the executive director with the Portland Streetcar. “Beyond that our ability to determine whether an animal is a service dog or not is really, really limited.”

While the investigation continues, the pit bull is lodged at the Multnomah County Animal Services.

A microchip in the pit bull was traced to an owner in Colorado who said she wants him back, said Mike Oswald, the animal services director.

The dog has been missing since June, Oswald said the owner told him.

The shelter has tried to get in contact with the person who had the pit bull on the streetcar but has not yet heard back, he said.

The “dangerous dog” investigation has four different levels, based on the severity of injuries, with fees and fines up to $500. If a dog is deemed dangerous, there are other restrictions and conditions for continued ownership, possibly including signs and muzzles.